1. Field of the Invention
The present invention relates to a pulley device and more particularly to a pulley device preferably adapted to be used in a belt driven stepless transmission apparatus.
2. Description of the Prior Art
Such a pulley device has been known as having a shaft provided at one end thereof with a disk extending radially outwardly therefrom, a tubular member enclosing the shaft, and being provided at one end thereof with a disk extending radially outwardly therefrom and cooperating with the disk of the shaft to define therebetween an annular groove having a V-shaped cross-section so as to receive a driving belt, and a rotating key extending axially in engagement with both of the shaft and the tubular member so as to prevent a relative rotation thereof. In these known pulley devices, the rotating key undergoes a large mechanical friction in an axial direction thereof, as well as in a rotational direction around its axis. A wear caused by such friction results in a heavy impact and vibration, so that a loss in the torque transmission is increased and a durability of the pulley device is impaired.
In order to avoid these problems, Japanese Patent No. 277496 (Japanese Pat. Publication No. 17504/61) proposes a pulley device in which an elastic member having a shock absorbing and abraison resistant elastic surface is disposed between the shaft and the key engaging the tubular member so as to prevent the rotating key to undergo the mechanical friction in the rotational direction. In this pulley device, however, the torque transmission loss is undesirably increased due to the presence of the elastic member between the shaft and the tubular member. In addition, the rotating key is worn rapidly because no specific consideration is made to the rotating key so as to avoid the mechanical friction in the axial direction thereof.